Problem: 4 folders cost $4.72. Which equation would help determine the cost of 5 folders?
There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 4 folders. We want to know the cost of 5 folders. We can write the numbers of folders as a proportion: $\dfrac{4}{5}$ We know 4 folders costs $4.72. We can let $x$ represent the unknown cost of 5 folders. The proportion of these costs can be expressed as: $\dfrac{\$4.72}{x}$ The cost changes along with the number of folders purchased, and so the two proportions are equivalent. $\dfrac{4}{5} = \dfrac{\$4.72}{x}$